The present invention relates to a radar method for measuring distances between and relative speeds of a vehicle and one or more obstacles.
From the related art of German Patent No. 42 44 608 A1, incorporated herein by reference, a continuous wave (xe2x80x9cCWxe2x80x9d) radar method is known in which the transmission signal generated by an oscillator is split up into constant-frequency, unspaced consecutive bursts (signal portions). In this case, the receiving signal reflected at an obstacle is mixed down with the transmission signal to baseband in a two-channel IQ mixer. The IQ mixer supplies a complex, relatively low-frequency mixer output signal, which is used for acquiring signals for the distances and relative speeds of a plurality of obstacles.
In the described method, four measurements are conducted with different transmission signals during a measuring cycle. In a first measurement, the oscillator chronologically generates consecutive bursts having a frequency which linearly increases in an incremental manner from a minimum to a maximum value. Subsequently, in a second measurement the oscillator generates a sequence of bursts having a frequency which linearly decreases in an incremental manner from a maximum value to a minimum value. In both measurements, a complex sampling value is acquired at the end of each reflected burst, and through mixing with the transmission signal bursts, first and second in-phase and quadrature-phase signals, respectively, are acquired for the distances and relative speeds. During a third measurement, the transmission signal is composed of bursts having the same frequency. At the end of each reflected burst, a complex sampling value for acquiring third in-phase and quadrature-phase signals for the relative speeds of the vehicle and the obstacle is obtained through mixing with the transmission signal bursts. In this case, a series of bursts having a monotonically rising or falling slope or frequency curve are designated altogether as a chirp.
Using Fourier transforms, all mixer output signals of the described first three measurements are converted into frequency values which are a function of relative speed and distance, and represent three sets of straight lines intersecting each other in a distance-relative speed diagram, the intersections of these lines representing potential obstacles. Those potential obstacles may be actual obstacles or ghost-obstacles generated through mathematical combination. Thus, in a fourth measurement, a transmission signal is emitted during a fourth measurement, whose bursts, however, do not follow each other monotonically, but are arranged according to the coefficients of a residual class code. The receiving signal reflected during the fourth measurement is composed of the superposition of all object reflections having different amplitudes and phases.
The correctness and single-valuedness of all intersection parameters of the lines in the distance-relative speed diagram, which result from the first three measurements, are tested by generating, for each of the potential obstacles, a setpoint mixer output signal for the fourth measurement""s transmission signal, the setpoint mixer output signal then being correlated with the actual mixer output signal of the fourth measurement. The special correlation properties of the residual class codes provide a high correlation value only for real obstacles and provide a low correlation value for ghost-obstacles.
The correlation begins with the obstacle having the highest amplitude. If a real obstacle is detected, then the corresponding setpoint mixer output signal is subtracted from the actual mixer output signal and the correlation continues in order of decreasing amplitude. The setpoint mixer output signal""s normalized amplitude is used during the correlation but only the phase portion of the complex signals is considered.
However, the IQ mixer used in the known method to acquire in-phase and quadrature-phase signals can cause a number of errors including, for example, offset errors, distortion of the modulation signal at the I and Q outputs, asymmetries of the I and Q output sensitivity, and orthogonal errors between the I and Q outputs, so that a complicated pretreatment of the radar data in the time interval, and an error calibration, are necessary.
German Patent No. 195 38 309 A1, discloses a generic radar method in which the form of the transmission signal and the manner in which the measured signals are evaluated are essentially implemented in a manner described previously in German Patent No. 42 44 608 A1. However, using the emitted transmission signals, the receiving signals reflected at the obstacles are demodulated here by only a one-channel mixer, whose output signal is not the signal of a phase-separated amplitude curve. This, in turn, forms the basis of a signal evaluation, in which target parameters can be ascertained from the transmission signal by using a modulated form of the transmission signal, with the aid of noncomplex, sampled raw radar data and these target parameters can be classified as right or wrong.
A further disadvantage of the above-mentioned evaluation procedure is that the ghost obstacles are only eliminated using the special correlation coding. This can result in a high error rate in the case of a plurality of obstacles, since the ghost obstacles cannot be reliably suppressed due to their usual high numbers.
The present invention provides a method and device for further simplifying the known CW radar method to evaluate the mixer output signal quickly, and at the same time, reliably.
The present invention provides a radar device or method for measuring distances between and relative speeds of a vehicle and one or more obstacles, in which a transmission signal (s(t)) is emitted, which is generated using an oscillator (1) and has a sequence of linear chirps (A, B, C, D); in which a receiving signal (e(t)) reflected at the obstacles (5) is simultaneously received during the emission of the transmission signal (s(t)); in which the receiving signal (e(t)) is mixed with the transmission signal (s(t)) in a mixer (6) for acquiring a mixer output signal (m(t)); and in which the mixer output signal (m(t)) is processed in a signal processing device (9) to obtain signal values for the distances (Ri) of the obstacles (5) to the vehicle, and for the relative speeds (vRel,i) of the vehicle and the detected obstacles (5); the mixer output signal (m(t)) for each chirp (A, B, C, D) of the transmission signal (s(t)) being analyzed using a Fourier transform, and the frequency positions Ki of the obstacles (5) being calculated as peaks in the Fourier transform spectrum; wherein a sequence of the transmission signal (s(t)) has at least four consecutive chirps (A, B, C, D) having the slopes (m1, m2, m3, m4), respectively, which are different from those of the other chirps (A, B, C, D); in the distance-relative speed diagram, the intersection points (Ri, vrel,i) of all the lines from two chirps (A, B) are calculated from all of the ascertained frequency positions K1,n and K2,p; a first condition is checked to determine whether a peak in the Fourier spectrum of the third chirp (C) exists at a frequency position K3,q, whose assigned line in the distance-relative speed diagram intersects a surrounding area of the intersection point (Ri, vrel,i); a second condition is checked to determine whether a peak in the Fourier spectrum of the fourth chirp (D) exists at a frequency position K4,r, whose assigned line in the distance-relative speed diagram intersects a surrounding area of the intersection point (Ri, vrel,i); and the intersection points (Ri, vrel,i) are then regarded as valid, when they fulfill both conditions.
Another embodiment of the present invention provides for a method or device, as described in any of the embodiments described herein, in which the intersection points (R1, vrel,i) of all lines from the first two chirps (A, B) are calculated from all the ascertained frequency positions K1,n and K2,p according to the equations             R      i        =          Δ      ⁢              xe2x80x83            ⁢              R        ·                                            κ                              2                ,                p                                      -                          κ                              1                ,                n                                                                        m              1                        -                          m              2                                                and    ⁢          /        ⁢    or                      v                              Re            ⁢                          xe2x80x83                        ⁢            l                    ,          i                    =              Δ        ⁢                  xe2x80x83                ⁢                  v          ·                                                                      m                  1                                ⁢                                  κ                                      2                    ,                    p                                                              -                                                m                  2                                ⁢                                  κ                                      1                    ,                    n                                                                                                      m                1                            -                              m                2                                                          ,  
where xcex94R signifies the distance resolution and xcex94v signifies the resolution of the speed.
A further embodiment of the present invention provides a method or device, as described in any of the embodiments described herein, wherein the calculated intersection points (Ri, vRel,i) are checked to determine whether a peak in the Fourier spectrum of a third chirp (C) exists at a frequency position K3,q, for which             k              3        ,        q              -          ϵ      1        ≤      (                            v                                    Re              ⁢                              xe2x80x83                            ⁢              l                        ,            i                                    Δ          ⁢                      xe2x80x83                    ⁢          v                    -                        m          3                ·                              R            i                                Δ            ⁢                          xe2x80x83                        ⁢            R                                )    ≤            k              3        ,        q              +          ϵ      1      
is valid, where xcex51 represents a parameter of predefined magnitude.
A further embodiment of the present invention provides a method or device, as described in any of the embodiments described herein, wherein the intersection points (Ri, vRel,i) are checked to determine whether a peak in the Fourier spectrum of a fourth chirp (D) exists at a frequency position K4,r) for which             k              4        ,        r              -          ϵ      2        ≤      (                            v                                    Re              ⁢                              xe2x80x83                            ⁢              l                        ,            i                                    Δ          ⁢                      xe2x80x83                    ⁢          v                    -                        m          4                ·                              R            i                                Δ            ⁢                          xe2x80x83                        ⁢            R                                )    ≤            k              4        ,        r              +          ϵ      2      
is valid, where xcex52 represents a parameter of predefined magnitude.
A further embodiment of the present invention provides a method or device, as described in any of the embodiments described herein, wherein the values of the parameters xcex51 and xcex52 are in the range of 0.3 to 0.7, preferably in the range of 0.4 to 0.6, and preferably 0.5.
The present invention generates at least four sets of lines in the distance-relative speed diagram. A valid intersection, therefore a real obstacle, can then be more reliably detected when four of the lines, each belonging to one of the chirps, form a common intersection which, because of existing measuring accuracies, is then designated as valid when all four lines intersect a predefined area segment in a distance-relative speed diagram. This area segment is defined by calculating the intersection of two lines and forming a surrounding range around it, through which the two other lines must pass. This surrounding range is also designated mathematically as the xcex5-range, xcex5 being a parameter for the size of the surrounding range.
Consequently, the intersections are checked twice, so that only a small proportion of ghost targets is still present in the detected and tested intersections. In this context, the evaluation procedure is not only reliable, but also can be implemented quickly because of the simple mathematical equations. The correlation coding known from the related art is no longer necessary.
The present invention is also described in German Application No. 199 15 484, filed on Apr. 7, 1999, from which the present invention claims priority.
Additional advantageous refinements of the present invention are cited in the dependent claims. An exemplary embodiment of the radar method or device according to the present invention is described below in detail using the included figures.